Hormonal Contraception and Endometrial Thickness in IVF/ICSI Cycles: A Multicentre Historical Cohort Study

To study the association between previous use of levonorgestrel intrauterine system (LNG-IUS) and endometrial thickness (EMT) in women undergoing in vitro fertilisation (IVF)/intracytoplasmic sperm injection (ICSI) cycles.

Multicentre historical cohort study.

Eight Danish public and private fertility clinics.

12786 women aged 18-46 years contributing with an EMT measurement from 22 464 different IVF/ICSI treatment cycles between 2000 and 2021.

Exposure was previous use of LNG-IUS, combined oral contraceptive pills (OCPs), progestogen-only pills (POPs), no/other contraception or combined, cumulated use of contraception when more contraceptives had been used during the inclusion period. LNG-IUS use was categorised into 0-3 years, >3-6 years, >6-9 years and >9 years. Mixed effect logistic regression adjusted for age, BMI, smoking, educational level, total FSH dose and fertility clinic was used.

EMT (< 7 mm vs >= 7 mm).

Statistically significantly higher odds of EMT >= 7 mm were found for OCPs [OR 3.53 (95% CI 1.29-9.65)], POPs [OR 6.43 (95% CI 1.45-28.63)] and no/other contraception [OR 6.67 (95% CI 2.37-18.74)] relative to LNG-IUS in IVF/ICSI cycles. All duration categories of ever use of LNG-IUS were associated with significantly lower odds of EMT >= 7 mm compared to no/other contraception.

Previous use of LNG-IUS was associated with decreased endometrial growth in women undergoing IVF/ICSI.